Do not define $GEM_HOME

Defining it breaks gems for all users who neither use RVM nor rbenv,
but have a different default Ruby version nonetheless.

Signed-off-by: Sorin Ionescu <sorin.ionescu@gmail.com>
Use correct option for pacman search aliases
Stop module loading when external code fails to source
Comment an unnecessary style
[Fix #477] Add instructions for updating Prezto
[Fix #479] Start only one ssh-agent instance
Merge remote-tracking branch 'upstream/master'

* upstream/master:
  [Fix #479] Start only one ssh-agent instance
  [Fix #477] Add instructions for updating Prezto
  Comment an unnecessary style
  Stop module loading when external code fails to source
  Use correct option for pacman search aliases
  Do not define $GEM_HOME